title: CD44 promotes progenitor homing into the thymus and T cell maturation.
abstract: Regain of immunocompetence after myeloablation and bone marrow cell (BMC) reconstitution essentially depends on T progenitor homing into the thymus and intrathymic T cell maturation. CD44 facilitates progenitor homing and settlement in the bone marrow and is known as a T progenitor marker. In search for improving regain of immunocompetence after BMC reconstitution, we explored whether the CD44 standard (CD44 s) and/or variant isoforms CD44v6 and CD44v7 contribute to thymus repopulation and thymocyte maturation. Antibody-blocking studies and cells/mice with a targeted deletion of CD44v6/7 or CD44v7 revealed that CD44s, but not CD44v6 and CD44v7, has a major impact on progenitor cell homing into the thymus. Instead, CD44v6 strengthens apoptosis resistance and expansion of early thymocytes. CD44v6-induced apoptosis resistance, most strong in double-negative (DN) thymocytes, is accompanied by Akt activation. CD44v6-induced proliferation of DN cells proceeds via activation of the MAPK pathway. At later stages of T cell maturation, CD44 acts as an accessory molecule, initiating and supporting TCR/CD3 complex-mediated signal transduction in double-positive and single-positive thymocytes. Thus, CD44 plays a major role in thymus homing. In addition, CD44v6 is important for survival and expansion of early thymocytes. These findings suggest that strengthening CD44v6 expression on lymphoid progenitors could well contribute to accelerated regain of immunocompetence.
authors.affiliation: Tumor Cell Biology, Department of Surgery, University of Heidelberg, German Cancer Research Center, Heidelberg, Germany.
authors.forename: Mohini
authors.initials: M
authors.lastname: Rajasagi
authors.forename: Mario
authors.initials: M
authors.lastname: Vitacolonna
authors.forename: Bojan
authors.initials: B
authors.lastname: Benjak
authors.forename: Rachid
authors.initials: R
authors.lastname: Marhaba
authors.forename: Margot
authors.initials: M
authors.lastname: Zöller
mesh_terms: D000818:Animals; D000906:Antibodies / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects; D002454:Cell Differentiation / Q000187:drug effects; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D018925:Chemokines / Q000378:metabolism; D018960:Hyaluronan Receptors / Q000276:immunology* / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D019707:Receptors, Chemokine / Q000378:metabolism; D016201:Receptors, Lymphocyte Homing / Q000276:immunology*; D015398:Signal Transduction / Q000187:drug effects; D013234:Stem Cells / Q000166:cytology* / Q000187:drug effects; D013601:T-Lymphocytes / Q000166:cytology* / Q000187:drug effects / Q000201:enzymology; D013950:Thymus Gland / Q000166:cytology* / Q000187:drug effects / Q000201:enzymology
chemical_list: D000906:Antibodies; C112697:CD44v6 antigen; C476399:Cd44 protein, mouse; D018925:Chemokines; D018960:Hyaluronan Receptors; D019707:Receptors, Chemokine; D016201:Receptors, Lymphocyte Homing; D020928:Mitogen-Activated Protein Kinases